package com.hmdp.utils;

import cn.hutool.core.util.BooleanUtil;
import cn.hutool.core.util.StrUtil;
import cn.hutool.json.JSONObject;
import cn.hutool.json.JSONUtil;
import org.springframework.data.redis.core.StringRedisTemplate;

import java.time.LocalDateTime;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.function.Function;

import static com.hmdp.utils.RedisConstants.LOCK_SHOP_KEY;

public class CacheClient {

    private final StringRedisTemplate stringRedisTemplate;

    public CacheClient(StringRedisTemplate stringRedisTemplate) {
        this.stringRedisTemplate = stringRedisTemplate;
    }

    // 写入缓存
    public void set(String key, Object value, Long time, TimeUnit unit){
        stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(value), time, unit);
    }

    //逻辑过期解决缓存击穿
    public void setWithLogicalExpire(String key, Object value, Long time, TimeUnit unit){
        // 封装逻辑过期时间
        RedisData redisData = new RedisData();
        redisData.setData(value);
        redisData.setExpireTime(LocalDateTime.now().plusSeconds(unit.toSeconds(time)));
        // 写入redis
        stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(redisData));
    }

    // 缓存穿透工具类
    public <R, ID> R queryWithPassThrough(
            String keyPrefix, ID id, Class<R> type, Function<ID, R> dbFallback, Long time, TimeUnit unit) {

        String key = keyPrefix + id;
        // 1.从redis查询缓存
        String json = stringRedisTemplate.opsForValue().get(key);
        // 2.判断是否存在
        if (StrUtil.isNotBlank(json)) {
            // 3.存在，直接返回
            return JSONUtil.toBean(json, type);
        }
        //判断命中的是否是空字符串 ""
        if (json != null) {
            return null;
        }

        // 4.不存在，根据id查询数据库 即shopJson == null，说明redis中的缓存过期
        R r = dbFallback.apply(id);

        // 5.数据库不存在，返回错误
        if (r == null) {
            //将空值写入redis
            stringRedisTemplate.opsForValue().set(key, "", RedisConstants.CACHE_NULL_TTL, TimeUnit.MINUTES);
            return null;
        }
        // 6.存在，写入redis
        this.set(key, r, time, unit);
        // 7.返回
        return r;
    }

    //逻辑过期解决缓存击穿
    private static final ExecutorService CACHE_REBUILD_EXECUTOR = Executors.newFixedThreadPool(10);

    public <R,ID> R queryWithLogicalExpire(
            String keyPrefix, ID id, Class<R> type, Function<ID, R> dbFallback, Long time, TimeUnit unit) {
        String key = keyPrefix + id;
        // 1.从redis查询商铺缓存
        String json = stringRedisTemplate.opsForValue().get(key);
        // 2.判断是否存在
        if (StrUtil.isBlank(json)) {
            // 3.不存在，直接返回null
            return null;
        }

        //4.命中，把json反序列化为对象
        RedisData redisData = JSONUtil.toBean(json, RedisData.class);
        R r = JSONUtil.toBean((JSONObject) redisData.getData(), type);
        LocalDateTime expireTime = redisData.getExpireTime();

        // 5.判断是否过期
        if (expireTime.isAfter(LocalDateTime.now())) {
            //未过期，直接返回
            return r;
        }
        //已过期，需要缓存重建
        //6.重建缓存
        //获取互斥锁
        String lockKey = LOCK_SHOP_KEY + id;
        boolean isLock = tryLock(lockKey);

        //判断获取锁是否成功
        if (isLock) {
            //获取锁成功，开启独立线程，实现缓存重建
            CACHE_REBUILD_EXECUTOR.submit(() -> {
                //重建缓存
                try {
                    //查询数据库
                    R rr = dbFallback.apply(id);
                    //写入redis
                    this.setWithLogicalExpire(key, rr, time, unit);
                } catch (Exception e) {
                    throw new RuntimeException(e);
                } finally {
                    //释放锁
                    unLock(lockKey);
                }
            });
        }
        //返回过期的商铺信息
        return r;
    }

    private boolean tryLock(String key) {
        Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(key, "1", 10, TimeUnit.SECONDS);
        return BooleanUtil.isTrue(flag);
    }

    private void unLock(String key) {
        stringRedisTemplate.delete(key);
    }
}
